1. Field of the Invention
The present invention relates to an improvement in an aluminum rotor for a compressor of a vane rotary type, and in particular, it is concerned with a method of forming an oil groove for preventing adhesion in a light aluminum alloy rotor.
2. Description of the Prior Art
A rotor of a compressor used for car air conditioners has a plurality of vane grooves through which vanes slidably move as shown in FIG. 1, and is consolidated in one body with a rotary shaft. The rotor is revolved while being slidably moved on the inner wall surfaces of side plates fixed to both sides of a cylinder block. A refrigerant gas is drawn in a compression space partitioned by five components of the rotor, vane, cylinder block and both side plates, and is then compressed and discharged. Since the compression space requires air-tightness it is designed so that these components have very small clearances among them, and in particular, when the rotor and side plates are slidably moved under compressive force, adhesion tends to take place between them.
Up to the present time, steel materials or ferrous sintered alloys have been used as the rotor and flake graphite cast iron or ferrous sintered alloys have been used as the side plate. In combinations of ferrous materials, the problem of adhesion is not serious since the materials are relatively excellent in wear resistance and the flake graphite cast iron or sintered alloys are excellent in oil retention. As occasion demands, an oil groove has been provided on one side surface or both side surfaces of a rotor to prevent such adhesion.
Of late, it has been studied to convert the material of a compressor from ferrous materials to aluminum, with the increased necessity for realizing a light weight compressor. Thus, it has been rendered possible to make a rotor of aluminum, for which aluminum could not be used up to the present time, by development of a powdered aluminum alloy consisting of a quenched and solidified powder and a high strength aluminum material, with the progress of the continuous casting technique. As to the side plate, the conversion of the material thereof into aluminum has also been possible by the use of high silicon aluminum materials such as A 390 material (commercial name). These alloys are not sufficient in adhesion resistance between the rotor and side plate in spite of the fact that large amounts of alloying components such as Si, etc. are contained therein so as to improve the wear resistance and adhesion resistance and to maintain the clearance precision at a high level. In particular, since adhesion tends to readily occur in a case where oil is exhausted on the sliding surface, an oil groove is necessary at the end surface of the rotor.
Since in the case of a rotor of an aluminum alloy, it is impossible to form an oil groove during powder compacting as in the case of the prior art rotors of sintered ferrous materials, because of the restriction on the production method, a step of working the oil groove should nevertheless be newly added. As the working method, an end mill or discharge working can be taken into consideration, but these methods have a problem that the installation thereof is of high rank and the working cost is too high. Furthermore, in the end mill working, the degree of freedom for imparting a groove shape is small.